Ten is perfect.

Any conversation about Kelly Slater begins with the number 10. As in, 10 Association of Surfing Professionals World Championships, the last of which he earned in November. Chop his career in half, and he’d still be both the winningest and second-winningest pro surfer in history. At age 20, he was the youngest world champion ever; at 39, he’s the oldest. In other words, there’s no point in comparing Slater with those in his own profession. By 2009, when Surfer magazine named him the greatest surfer of all time, it had already become a parlor game to measure his career stats against athletes like Michael Jordan and Tiger Woods. But he is different.

Of course, grade-A athleticism is a big part of what makes Slater great. Go to YouTube and watch a few of his clips. Megadoses of speed, strength, balance and flexibility, perfectly combined — the raw talent wafts off the screen like pheromones.

But Slater takes things a step further. See that clip from the 2008 Rip Curl Pro Search event, in Bali? There’s a bit near the end where he pops out of the tube at a grinding reef break called Padang Padang, swoops down to the trough, turns, changes stance from his usual left foot forward to right foot forward, then casually tucks back into another tube section. Nobody does that.

Switching stance halfway through a ride, during a big contest, on that type of wave, is like jumping from the roof of one moving car to another during an ice storm. “I figured if I pulled in normally, I would have gotten a 7,” he shrugged afterward. “Ithought I might as well have some fun.”

Slater loves improv. Just makes stuff up on the fly. He’s a fantastic showman, just this side of a show-off. That counts for a lot in surfing, which much of its rank and file, perhaps a majority, still resist seeing as a serious sport. True, Slater has worked hard at his career. He’s obsessively, maybe pathologically, competitive. But he makes a point, too, of having a good time on the way to the winner’s stand. This magnifies his appeal, even to opponents. The voices you hear in the background on that Bali clip, laughing and groaning in amazement — those are world-tour pros, globe-trotting seen-it-all dudes who nonetheless fix their attention on Slater like the rest of us fans, waiting for him to conjure up another miracle.

In January, the surf media and blogosphere flared up briefly on the topic of whether Slater should retire from competition or keep going. Slater himself has been coy on the subject. He has entered the opening event of the year, in Queensland, Australia, but hasn’t committed to the full 2011 tour. “I don’t know if that’s the tip of the mountain,” he told Surfer a few weeks before winning his 10th title, “or just a stop along the way.”

It’s been pointed out that a lot of the people who want Slater to continue are older surfers, people who need him out there performing for the same reason a few million baby boomers need the Rolling Stones out there performing — because, illusion or not, it keeps the flame of youth alive.